In the most advanced fields of the current technology there is an increasing demand for articles, also of micrometric dimensions, which combine characteristics of different materials. Consequently there is a great demand for new technologies for connection in a stable manner and/or in selected areas of materials which are chemically different. The processes proposed so far, however, are not always able to guarantee satisfactory results.
In particular, in the field of microfluidics, the production of microvalves having an element in silicone connected to a support made of a different material is extremely important.
The bond between the silicone membrane and the support, which is usually connected to microfluidic channels, can be achieved by different methods. In said regard, thermal bonding [L. Brown, et. al., Lab on a Chip 2006, 6, 66-73], the use of appropriate adhesives and furthermore the use of dopants have been proposed to modify the properties of materials.
Nevertheless, the possibility of connecting the parts in question by the formation of irreversible chemical bonds is still unexplored in this sector. This is due partly to the difficulty of promoting the chemical interaction between phases, the affinity of which is, by nature, negligible, and partly to the numerous problems that arise concerning the production process.
A barrier to the formation of chemical bonds between the support (for example in PMMA) and the silicones is represented by the elastomers which are chemically inert and strongly hydrophobic. The increase in the surface tension of the silicones can be modulated by plasma treatments or by corona discharge (see for example Kathryn Haubert, Tracy Drier and David Beebe Lab Chip, 2006, 6, 1548-1549; BHATTACHARYA Shantanu; DATTA Arindom; BERG Jordan M.; GANGOPADHYAY Shubhra Journal of microelectromechanical systems 2005, vol. 14, no 3, pp. 590-597). However, the results obtained have shown little effectiveness.
In many applications [Microchemostat—microbial continuous culture in a polymer-based, instrumented microbioreactor Zhang, Z.; Bocazzi, P.; Choi, N. G.; Perozziello, Gerardo; Sinskey, A. J.; Jensen, K. F. LAB ON A CHIP (ISSN:), vol: 6, issue: 7, pages: 906-913, 2006] surface modification of the PMMA is necessary to prevent cellular adhesion [S. Patel et al./Biomaterials 27 (2006) 2890-2897].
Furthermore, for many other applications it is important to obtain selective adhesion of a material on a substrate [Ultrathin poly(ethylene glycol) monolayers formed by chemical vapor deposition on silicon substrates—SHIRAHATA Naoto; HOZUMI Atsushi Journal of nanoscience and nanotechnology (J. nanosci. nanotechnol.) Self-Assembled Nanomaterials 2006, vol. 6, no 6 (50 ref.), p. 1695-1700]. Examples in this regard are optical guides [Lim, H. M: Murphy, T. E. J. Vac. Sci. Technol. B 17(6), November/December 1999] and the deposition of SAM [Yu, A. A. Savas, T JACS 127 (2005) 16774-16775]. More generally, all processes of partial functionalisation of surfaces by means of primers are performed using selective masks.
However, the use of masks during the deposition phase makes the process more complex in some cases. In addition to a greater number of operations of the process itself, the mask must be carefully designed in terms of dimensions (thickness, oversizing of the exposed zones to compensate the shadow effects) and component material. This must be compatible as far as possible with the characteristics of the material to be deposited in order to prevent their incompatibility producing shadow zones.